The drive means to which the present document relates comprise at least one of each of the following elements;
a reversible internal combustion engine, PA1 a step-down geartrain driven by the engine, PA1 a friction-type clutch allowing the engine to be decoupled from the step-down geartrain, PA1 a shaft line driving a screw propeller with fixed blades, and PA1 a friction-type brake allowing the shaft line to be decelerated and held stationary. PA1 maneuvering (dead slow) ahead and astern, PA1 running ahead, from a standstill to full speed, PA1 braking and stopping the ship in a minimum distance, a situation known as a "crash-stop", PA1 sudden unavailability of one engine where the drive mechanism comprises a plurality of engines. PA1 choosing a desired speed for the ship, PA1 measuring the present speed of the ship and the parameters representing the operation of the engine, geartrain, brake, clutch, and screw, PA1 and comprising the additional steps consisting of: PA1 said values of said performance limits for the engine, the brake and the clutch are calculated before sending each state-changing command, said calculation consisting, for the engine, in determining the maximum torque which is potentially available and the law for obtaining this torque from the present state of the engine, and, for the clutch and the brake, in determining the amount of heat energy which can still be carried by these components, taking into account their present thermal state and the number of operations which they have already performed, PA1 a clutch engagement operation is performed at the same time as an operation in which engine torque is increased, so as to allow said engine torque to establish itself whilst minimizing the heat energy generated by the clutch.
The speeds ahead and astern of ships fitted with a drive mechanism of this type are controlled by acting on the speed and the direction of rotation of the engine and therefore of the screw, and any change of those two parameters may require combined or successive operation of the clutch and the brake. Changing the speed of the engine requires the load which will be imposed on the engine after it has changed speed to be predicted, it being evident that a load greater than the available engine torque could cause the engine to stall. Operating the brake and the clutch causes a portion of the mechanical power which they convey to be transformed into heat. If the heat dissipation limit is exceeded, then the torque transmissible by those members diminishes, this being followed by irreversible damage to some of their component parts.
Numerous parameters must therefore be taken simultaneously into account in order to control the ship, this being complicated even further if the drive mechanism comprises, for example, two engines driving a single shaft line via a step-down geartrain which transmits power from one or both engines to the shaft line. In this case, depending on the set speed, one of the engines may, for example, be disengaged and stopped.
The most frequently encountered situations and ship speeds are as follows: